An injection molding apparatus has as main components a bed, a mold-clamping mechanism mounted to the bed, and an injection machine mounted to the bed. A molded article is obtained by clamping a mold through use of the mold-clamping mechanism and injecting a resin material into the mold from the injection machine.
Mold-clamping mechanisms of various designs are known (see Japanese Patent No. 5426142, for example).
The structure of a pressure-receiving platen disclosed in Japanese Patent No. 5426142 is illustrated in FIG. 12 hereof. As illustrated in FIG. 12, in a tailstock 200 corresponding to a pressure-receiving platen, a portion corresponding to a ceiling part is configured from a horizontal beam 202 of a forward rectangular part to which toggle link connecting parts 201 are integrally provided, a horizontal beam 203 of a rearward rectangular part, and a load-transmitting bottom part 204 for joining the beam 202 and the beam 203. A bottom part disposed below the ceiling part has the same structure.
A force applied to the horizontal beam 202 of the forward rectangular part is transmitted through the load-transmitting bottom part 204 to the horizontal beam 203 of the rearward rectangular part. The horizontal beam 202 of the forward rectangular part, the load-transmitting bottom part 204, and the horizontal beam 203 of the rearward rectangular part are integrally formed, and rigidity thereof is therefore ensured. A reduction in wall thickness in the vicinity of the load-transmitting bottom part 204 also reduces the weight of the tailstock 200.
The conventional pressure-receiving platen is thus structured so as to have increased rigidity in order to withstand the force applied thereto via a toggle link. Specifically, the conventional pressure-receiving platen has the structure of a pressure-receiving platen 206 not having an opening, such as is illustrated in FIG. 8B described below. This pressure-receiving platen 206 can be considered to be a both-ends supported beam supported at both ends thereof by tie bars 207, 207.
When the force from the toggle link is applied to the center of the both-ends supported beam (pressure-receiving platen), the center flexes. Both ends are simply supported, and therefore incline in conjunction with the deformation of the center. The tie bars 207, 207 at this time are inclined at the same angle as the ends. At this time, the pressure-receiving platen is fixed to the bed, the inclination on the bottom-part side of the pressure-receiving platen is small, and the inclination on the ceiling-part side of the pressure-receiving platen is large. In a mold-clamping apparatus of a type in which force is transmitted via a toggle link, it is important for the stretching of the tie bars to be uniform, and the difference in inclination described above leads to a difference in the stretching of each tie bar. Inclination of the tie bars is therefore preferably reduced.
Conventionally, the rigidity of the pressure-receiving platen is increased in order to reduce inclination of the tie bars. Rigidity increases as wall thickness is increased, but this approach adds to the weight of the pressure-receiving platen, and the cost of the mold-clamping mechanism increases.
However, while reduction in cost of the mold-clamping mechanism is sought, there is a need for a mold-clamping mechanism structure capable of reducing inclination of the tie bars while being lighter in weight.